By David Chazan BBC News

United States officials say they believe a Somali-based Islamic group may have carried out Thursday's twin attacks on Israeli targets in the Kenyan city of Mombasa.

The officials say the group, Al-Ittihad al-Islamiya - also known as the Islamic Union - is a prominent militant organisation in the Horn of Africa with links to Osama Bin Laden's al-Qaeda network.

The group may have targeted US soldiers in Somalia

Al-Ittihad was placed on the US list of terrorist groups after the 11 September attacks, but for the Americans, al-Ittihad is an old enemy.

Intelligence officials have suggested that it may have had a hand in the downing of two American helicopters in the Somali capital Mogadishu in 1993.

But that is strongly denied by members of other Somali militias which were also fighting the Americans.

Weakened

The group is thought to have begun operating in the 1990s.

The Americans say it has been financed by Osama Bin Laden and has about 2,000 members.

But European intelligence agencies and Somali sources say al-Ittihad has been severely weakened in recent years.

It was badly hit in fighting between rival Somali militias in the late 1990s.

And it has suffered repeated attacks by Ethiopian forces after being blamed for bombings in Ethiopia five years ago.

Teaching

Somali sources say al-Ittihad was a strong military force a few years ago but has now changed its tactics.

Many of its members have become teachers in the hope of recruiting young Somalis to the Islamist cause.

They have also gone into business, prompting accusations last year that Somalia's largest commercial enterprise, Al Barakaat, was funding terrorism.

But when the Americans shut down Al Barakaat, UN officials in East Africa said Washington had got the wrong target.

Al-Ittihad may no longer be an active military force, but it remains influential in its former stronghold in southern Somalia, along the porous border with Kenya, so it would certainly have been easy for its militants to reach Mombasa.